It's a good thing Moana has so many appealing performative qualities - the freshness and optimism of its animators' color palette and locations; the winning personalities of its voice cast; the joy of its singing and dancing - because otherwise, we might be tempted to pay too much attention to the actual story.

This is one of those movies so full of life on the outside that it's harder to notice - and then, harder to care - how mechanical its storytelling is, how we watch the wheels of the screenplay creak on and on, useful only for their ability to drive forward a narrative even as it ceases to be convincing or surprising. It's a movie salvaged by the simple fact that it's an animated musical, which at least makes its harmless banality easy on the eyes and ears. It may not have a lot of vigor underneath, but its shallow delights are persistently charming.

Granted, a heroic empowerment story like this one has a pretty simple path laid out in front of it. But even so, the specifics here have all the interest level of a Marvel plot - a thing was stolen, the hero has to find it and return it, and thus save the world (or, in this case, a Polynesian island ... which, as far as the movie's jurisdiction is concerned, is the world). Moana's emotional journey seems equally predetermined, with the characters' moments of growth or change coming more out of mechanical necessity than any real impetus. We have the heroine-in-training going out on her own for the first time, the reluctant protector (with motives of his own) by her side, and the animal sidekick providing the comic relief - and all behave in exactly the ways required, at the moments required. The film gets away with it because its voices and animators are too terrific to ignore.

The most interesting substantive detail is that the protagonist's coming-of-age has purpose far beyond herself, making this not just a story of growth but one of actual heroism. Fifteen-year-old Moana (voiced by Auli'i Cravalho) is the future chief of her beloved island of Motunui, with her father and current chief, Tui (Temuera Morrison), having spent years preparing her for the sacred duty of leading her people for generations to come. That comes with one rather large condition - that she should never leave the island. Going beyond the reef is far too dangerous, Tui insists. Even dipping her toes in the ocean water seems to be too much for him. Like all Disney protagonists, Moana has an adventurous spirit that can't be tamed no matter what her father says, and when her island faces hard times - as food becomes an unexpected scarcity - she has all the window she needs to defy Tui's rules, go beyond the reef and preserve the future of her people. As Moana learns more about her history, this passionate youthful venture deepens into a reclamation of cultural purpose and identity.

Substantively, though, that angle is mostly set dressing. It's the end game, but it has little to do with the journey. For that, we get a mismatched buddy movie - with Moana joined on her quest by a demigod, Maui (Dwayne Johnson), who's too busy boastfully soaking in his own self-declared greatness to care much about this teenage pest and her "important mission." It takes him a while to realize that he's an indispensable part of that mission, having years earlier stolen a goddess' heart (for purely magnanimous reasons, he insists) in an act that cursed the island and necessitated Moana's journey in the first place. Only he can return the heart to its rightful place and thus save Moana's people.

But neither he nor his eyebrows want to hear it. (His tattoos, on the other hand - a perpetually active, animated record of his accomplishments and moral conscience - are another matter entirely.)

The problem is not that we know he will change - that we know he'll be humbled and come around and eventually prove his valor - but that the film, in key moments, just has him change without any motivation to do so. Or, rather, the motivation is solely in the dramatic requirements of the situation. Jared Bush's screenplay knows how Maui is meant to function over the course of the story, but forgets to justify it when those key moments come. Change happens, but the script doesn't do the legwork to make it anything more than functional. Maui is a memorable character on the strength of the voice performance (Johnson's charisma bleeds over even when he's not on screen), and in the way he interacts with his tattoos, and in the expressive angles of his face. But as a part of the narrative, he's basically an automated response mechanism.

The title character's growth is often victim to the same screenwriting shortcuts, but once again it's the voice work that saves it; newcomer Cravalho is resolutely fearless in her energy, painting Moana with idiosyncratic mannerisms that naturalistically reflect the uncertainty of the journey in ways much of the film otherwise can't articulate. Not unlike Johnson's work, there are dynamite comic impulses to Cravalho's acting, even though her character only occasionally operates as a comedic instrument. It's one of the most impressive debut performances in recent years; she adds so much that might otherwise be missing from, or at least different about, the character.

With its clunky execution of well-worn story beats, Moana requires a lot of its other elements, and for the most part they are up to the task. (My only other gripe is relatively minor, and perhaps strictly personal. The emphasis of skin in the character and production design underlines a strange shortcoming in CG animation. There's an impression of animated "realism," for lack of a better word, in everything that surrounds the characters - the mountains, the trees, the ocean, the sand. Yet for the characters themselves, their skin still has this gelatinous, rubbery appearance that strikes an odd contrast with the more naturalized backgrounds. The characters are almost doll-like, as if molded into rigid plastic form. Again, it's not a game-changer, but the disconnect in sophistication between animate and inanimate is noticeable, in a way you don't see in the more environmentally consistent forms of stop-motion and hand-drawn. But I digress.)

If the trade-off for Moana's perfunctory plotting is spending more time exploring the character dynamics and indulging in the film's musical and action setpieces and digressions - including a chase/getaway sequence against a ship full of Fury Road-inspired pink masked pirate creatures, and a heist-turned-musical number courtesy of Jemaine Clement's Tamatoa, a giant crab who collects shiny things - then I'll take that trade. Lin-Manuel Miranda's music, Cravalho and Johnson's voices, and Ian Gooding's production design - and a prevailing sense of humor that knows exactly how to utilize all of the above - make the whole thing feel effortlessly rewarding.